In a method of this type, known for example from German Patent Application 1 704 091, it is provided to use, for every mold, an individual band of labels from which a label is cut by means of a die constituted by the edge of an access opening provided in the lateral wall of one half-mold and by means of a transversely movable punch, when the two half-molds are spaced apart to allow the passage of the container which has been thermoformed and when one of the half-molds is applied against the band of labels, the punch then stamping a label while transferring it towards the internal lateral face of the forming chamber of the half-mold and accompanying, in that position, the half-mold until the two half-molds are joined together. This manner of proceeding presents many disadvantages among which that of having to return the punch to its initial position rather far from the joining up position of the two half-molds, before the band of labels is released from said punch and can be moved forward one step. Another disadvantage resides in the stamping itself of the labels in the area of the access opening, this producing, after the stamping, a fragile grate-like pattern which, moreover, is used for transmitting to the band of labels the pulling force which controls the forward motion of the band. In this particular case, the label band moves according to a fixed path and it is the half-mold which is brought close to that path for the stamping operation.
To overcome, at least partly, this disadvantage, it has been proposed to make part of the path of a band fast with a half-mold and to associate all the labels stamping means to said mold (see for example U.S. Pat. No. 3,684,418). However, this also produces a fragile grate-like pattern and the punch prevents the label, band or strip from moving forward as long as said punch has not returned to its initial position.
Another disadvantage of the two known methods resides in the use of individual bands of labels, so that when simultaneously thermoforming several containers, it is difficult, if not impossible, to control with accuracy, with simple means, that all the bands move simultaneously the same length of step. This disadvantage has, on the whole, already been eliminated by either one of two similar proposals made for example in French Patents 2 034 915 and 2 403 117 whereby individual bands of labels are produced from a master band common to several individual bands and the moving step of all the individual bands is determined at the level of the cutting of the master band whereas a pair of feeding rollers is associated with each of the individual bands, the periphery laying out length of which rollers is more than the length of one step at the level of the cutting of the master band so that said rollers begin to slip when they have absorbed the length of a one-step forward motion given by the master band. It is easy to understand that this manner of proceeding cannot be applied to the known individual bands because the grate-like patterns, resulting from the stamping of the bands, would tear. This known control method cannot be used with molds composed of two horizontally moving half-molds and even less with molds that are vertically movable and of which the forming chambers are open upwardly and have a bottom which is either fixed or vertically movable, but which, in any case, is independent of the lateral wall of the forming chambers, due to the fact that in all these known systems, the length of the path of an individual band counted between the master band cutting zone and the pair of rollers advancing the individual band associated with a forming chamber, varies between two extreme values corresponding to an upper forming position and to a lower stripping position.
Yet another major disadvantage of the known methods resides in the fact that they do not permit the manufacture of two close together rows of containers from a horizontal thermoplastic band moving stepwise in a direction perpendicular to the plane traversing the axes of the containers of a container row.